This invention relates to a process for preparing cyclohexanone. More particularly, this invention relates to a process for preparing cyclohexanone by hydrogenating phenol in the presence of a catalyst, using as starting material phenol obtained from fractional distillation of cumene hydroperoxide decomposition product.
The process whereby phenol is hydrogenated directly and selectively to cyclohexanone is well known. It is also well known that certain impurities present in commercial phenol effect the hydrogenation process. For example, the presence of iron, sulphur, and halogen, has been known to reduce catalyst efficiency and adversely effect selectivity.
In an effort to overcome these problems, the prior art has suggested the use of special catalysts and has further suggested certain pretreatment purification techniques prior to hydrogenation. None of these have met with too great of a success even though phenol having a purity of 99.9 percent is obtainable. In this respect it should be noted that impurities present in phenol when used in one commercial application such as the preparation of phenolic resins are not particularly significant in hydrogenation procedures. Accordingly, certain of the impurities which effect the colour stability of phenol do not effect the hydrogenability of phenol and vice-versa. Another reason for this lack of success is that commerical phenol is derived from a variety of sources and the impurities contained therein are of process environmental origin. Thus phenol obtained from the distillation of coal tar, or from the hydrolysis of chlorobenzene or from the dehydrogenation of cyclohexanol, will contain impurities which are different from those contained in phenol prepared by the cumene hydroperoxide process.
The production of phenol from cumene is well known. A typical process for obtaining phenol from cumene hydroperoxide, which has been obtained by liquidphase oxidation of cumene with molecular oxygen, involves forming a reaction mixture by continuously feeding the cumene oxidation product containing at least about 80 percent by weight of cumene hydroperoxide into a decomposer wherein the incoming hydroperoxide is diluted by cumene hydroperoxide decomposition products previously formed therein, maintaining the reaction mixture at elevated temperature, feeding to the reaction mixture a decomposition catalyst selected from the group consisting of sulfur dioxide and sulfuric acid, withdrawing reaction mixture from the decomposer, removing the decomposition catalyst from the product withdrawn form the decomposer, and fractionally distilling the resulting organic products to separately recover on acetone fraction, a phenol fraction and one or more by-products fractions. Patents relating to purification of phenol obtained by decomposition of cumene hydroperoxide include U.S. Pat. Nos. 2,597,497; 2,881,222; 2,910,511; 3,187,050; 3,692,845; 3,830,708; 3,896,006; and 3,965,187.
It is also known that the single most detrimental impurity contributing to the poisoning of catalyst systems when phenol is hydrogenated, is the presence of a specific carbonyl compound formed along with phenol during manufacture from the decomposition of cumene hydroperoxide. This specific carbonyl compound is known as 1-hydroxy-2-propanone, hydroxyacetone or acetol. More specifically, when phenol is hydrogenated in the presence of hydroxyacetone, the effectiveness of a hydrogenation catalyst is greatly reduced. This reduction of effectiveness is noted in two ways, firstly, in that the hydrogenation rate is decreased, and secondly, in that the catalyst life is greatly diminished. The most pertinent prior art is believed to be U.S. Pat. No. 3,965,187 which discloses that the catalytic hydrogenation of phenol obtained by the cumene hydroperoxide process is improved by hydrogenating high purity phenol containing not more than 75 ppm of hydroxyacetone. Hydroxyacetone-free phenol is obtained by treating phenol for 1-5 minutes with a polyamine such as hexamethylene diamine, hexamethylene triamine and the like or an aqueous solution thereof, and then distilling the mixture to separate the components.
The process for hydrogenation of phenol to cyclohexanone as disclosed in U.S. Pat. No. 3,965,187 is an important contribution to this art; however, the poisoning of metallic catalysts, e.g., palladium catalysts, has not been entirely eliminated in large scale commercial processes due to long-term accumulation of impurities, particularly nitrogen-containing impurities such as tricyclohexylamine, phenylcyclohexylamine and dicyclohexylphenylamine. We have now discovered that such impurities result from nitrogen-containing decomposition products formed from the polyamines introduced in accordance with the process of U.S. Pat. No. 3,965,187.
The present invention obviates these problems by providing an improved method for hydrogenating phenol wherein the effectiveness of the catalyst is greatly prolonged and hydrogenation rate increased.